This invention relates in general to testing of materials by their thermal properties and in particular to the testing and measuring of the thermal and physical properties of bodies of solids and fluids by means of fiberoptic techniques.
Physical properties of solids and bodies of fluids have often been measured or tested through measuring or testing their thermal properties. In U.S. Pat. No. 4,344,322 Plapp discloses a device for measuring air flow rate using two hot wire resistors placed in the air intake tube of an internal combustion engine.
In U.S. Pat. No. 4,344,315 Moxon et al. disclosed a device for distinguishing between natural and simulated gems by testing their thermal conductivities. Moxon et al employ a test probe comprising a simple contacting head and a temperature sensing element mounted to a back surface of the head and in thermal contact thereto. The front surface of the contacting head is rounded and adapted to contact gems and has a certain thermal conductivity and hardness. An electrical circuit is connected to the temperature sensing thermistor in the temperature sensing element to provide an indication of temperature change when the heat source thermistor is energized and de-energized. When the round surface of the head is in contact with a gem to be tested, pulses of thermal power are cyclically applied to provide a predetermined amount of heat flow from the probe through the sample gem. The resulting change in temperature of the conducting head is determined by sensing the change in resistance of the sensing thermistor and weighting that change by the sensed thermistor resistance. The change in temperature signal controls a meter and LED which indicate whether the gem is natural or simulated.
The above described devices and methods as well as many other systems used in the prior art are electrical techniques utilizing thermocouples, thermistors or resistance thermometers by means of which electrical signals are generated and then converted into temperature readings or employed for control functions. It is sometimes essential, however, to test or measure the physical properties of materials through their thermal properties by non-electrical techniques. This may occur: (1) where temperatures over large areas are to be measured and measurement by a dense distribution of thermistors or thermocouples thus becomes impractical; (2) where the attachment of thermistors or thermocouples and leads would alter the temperatures to be measured; (3) in environments where because of high electromagnetic fields metallic wires are undesirable; (4) where electrical isolation is described such as in many medical applications; (5) where insensitivity to electrical noise generation is desired; (6) where, because of motion or remoteness of the part to be sensed, permanent lead wires are impractical; or (7) where, because of corrosive chemical environments, wire and thermal couple junctions would be adversely affected, with resultant changes in electrical characteristics. In these situations, optical techniques frequently become preferable. Furthermore, optical fibers may be preferable in many explosive or radioactive environments.
In U.S. Pat. Nos. 4,345,482 Adolfsson et al. disclose a fiberoptic device for measuring physical magnitudes such as force elongation, pressure acceleration and temperature. The device comprises a transducer unit and an electronic unit. The quantity to be measured is supplied to the transducer unit to affect the resonance frequency of an oscillating body included in the transducer unit by changing the dimensions, mass, density, modulus of elasticity and/or mechanical stress of the body. The oscillations of the body are detected optically by means of a fiberoptic position/movement detector. The electronic unit of the fiberoptic device then generates an output signal representative of the oscillations of the body and therefore measures the physical quantity.